Center for Advanced Radiotherapy Technologies and Department of Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, California 92093, USA.
Med Phys. 2013 Sep;40(9):091704. doi: 10.1118/1.4816677.
The aim of this work was to design a novel high-dose rate (HDR) ((192)Ir) brachytherapy applicator for treatment of rectal carcinomas that uses tungsten shielding for possibly improved dosimetric results over commercial brachytherapy applicator(s).
A set of 15 single-depth applicators and one dual-depth applicator were designed and simulated using Monte Carlo (MCNPX). All applicators simulated were high-density tungsten alloy cylinders, 16-mm in diameter, and 60-mm long, with longitudinal grooves within which an (192)Ir source can be placed. The single-depth designs varied regarding the number and depth of these grooves, ranging from 8 to 16 and 1-mm to 3-mm, respectively. The dual-depth design had ten channels, each of which had two depths at which the source could be placed. Optimized treatment plans were generated for each design on data from 13 treated patients (36 fractions) with asymmetrical clinical target volumes (CTVs). All results were compared against the clinically treated plans which used intracavitary mold applicator (ICMA), as well as a recently designed, highly automated, and collimated intensity modulation device named dynamic modulated brachytherapy (DMBT) device.
All applicator designs outperformed the ICMA in every calculated dosimetric criteria, except the total dwell times (∼30% increase). There were clear, but relative, tradeoffs regarding both the number of channels and the depth of each channel. Overall, the 12-channel, 1-mm depth, and 14-channel 2-mm depth designs had the best results of the simpler designs, sparing the healthy rectal tissues the most while achieving comparable CTV coverage with the dose heterogeneity index and lateral spill doses improving by over 10% and the contralateral healthy rectum dose dropping over 30% compared to ICMA. The ten-channel dual-depth design outperformed each single-depth design, yielding the best coverage and sparing.
New grooved tungsten HDR-brachytherapy devices have been designed and simulated. The results of this work attest to the capability of these new, highly anisotropic, intelligently shielded applicators to limit dose to healthy tissues while maintaining a conformal prescription dose to the CTV.
本研究旨在设计一种新型的高剂量率（HDR）((192)Ir)近距离放射治疗施源器，用于治疗直肠癌，该施源器采用钨屏蔽，以获得优于商业近距离放射治疗施源器的剂量学结果。
使用蒙特卡罗（MCNPX）模拟设计并模拟了一组 15 个单深度施源器和一个双深度施源器。所有模拟的施源器均为高浓度钨合金圆柱体，直径 16mm，长 60mm，纵向有凹槽，可放置((192)Ir 源。单深度设计在这些凹槽的数量和深度方面有所不同，分别为 8 到 16 个和 1 到 3mm。双深度设计有十个通道，每个通道有两个源可放置的深度。根据 13 例接受治疗的患者（36 个分次）的不对称临床靶区（CTV）数据，为每个设计生成了优化的治疗计划。所有结果均与使用腔内模具施源器（ICMA）治疗的临床计划以及最近设计的、高度自动化的、称为动态调制近距离放射治疗（DMBT）的准直调强装置进行了比较。
所有施源器设计在计算的所有剂量学标准中均优于 ICMA，除了总驻留时间（增加约 30%）。在通道数量和每个通道的深度方面都有明显但相对的权衡。总体而言，12 通道、1mm 深度和 14 通道 2mm 深度设计在更简单的设计中具有最佳结果，在实现与 ICMA 可比的 CTV 覆盖的同时，最大限度地保护健康直肠组织，剂量异质性指数提高超过 10%，对侧健康直肠剂量降低超过 30%。十通道双深度设计优于每个单深度设计，产生最佳的覆盖和保护。
新设计的带有凹槽的钨 HDR 近距离放射治疗施源器已设计并模拟。这项工作的结果证明了这些新的、高各向异性的、智能屏蔽施源器能够限制健康组织的剂量，同时保持对 CTV 的适形处方剂量。
